Traumatic brain injuries severely reduce the quality of life for affected individuals and carry significant societal and economic costs. Despite the prevalence of these injuries, there is currently no effective treatment. Here we propose to develop a novel treatment for permanent brain damage: an Adaptive Cognitive Prosthetic that will learn to replace the neural function that was lost due to a brain injury. To effectively bypas the damaged cortical region, our proposed cognitive prosthetic will mimic its structure: it will record neural activity from other brain regions, transform this activity according to the lost cognitive function, and then stimulate unaffected brain regions in order to convey the result. Here we propose to develop the three core components necessary for achieving such a prosthetic. First, neural activity must be recorded from unaffected brain regions. This will provid the input to the prosthetic, allowing it to monitor the current brain state. Second, the prosthetic must be able to act upon the brain, stimulating neural tissue in undamaged brain regions in order to bypass the damaged brain region. Finally, an adaptive algorithm must bridge the previous two components: transforming the observed brain state to a pattern of stimulation in order to mimic the to-be-replaced brain region. However, the exact pattern of stimulation previously associated with each state is unknowable and therefore must be learned. To this end, we propose a novel, hierarchical, learning algorithm that can discover the appropriate stimulation patterns. My lab is uniquely positioned to develop this prosthetic. We have extensive experience recording from large populations of neurons (the first component) and have developed a novel paradigm for stimulating patterns of neural activity (the second component). In the current proposal we will develop the adaptive algorithm, testing its efficacy in mice. Finally, we will combine all of the necessary components to test the cognitive prosthetic in a monkey-model of hemispatial neglect, a common behavioral deficit following parietal stroke.